GC seems to work with 12 bits.
tree6d1005f9a25360a3d07193b7c5902f7a87f4ce4e
-rw-r--r-- 12516 library.scm
-rw-r--r-- 57351 picobit-vm.c
-rw-r--r-- 104689 picobit.scm
-rw-r--r-- 388 red-green.scm
-rw-r--r-- 31529 robot.scm